<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>两个相同字符串之间的最长子字符串</title>
</head>
<body>
  <script>
    function fn(s) {
      let max = 0
      for (let i = 0; i < s.length; i++) {
        let last = s.lastIndexOf(s[i])
        if (last) {
          max = Math.max(max, last - i)
        }
      }
      return max - 1
    }
    console.log(fn('aa'))
  </script>
</body>
</html>